high CVSS 7.3

CVE-2026-33430·Python vulnerability

Briefcase is a tool for converting a Python project into a standalone native application. Starting in version 0.3.0 and prior to version 0.3.26, if a developer uses Briefcase to produce an Windows MSI installer for a project, and that project is installed for All Users (i.e., per-machine scope), the installation process creates an directory that inherits all the permissions of the parent directory. Depending on the location chosen by the installing user, this may allow a low privilege but authenticated user to replace or modify the binaries installed by the application. If an administrator then runs the altered binary, the binary will run with elevated privileges. The problem is caused by the template used to generate the WXS file for Windows projects. It was fixed in the templates used in Briefcase 0.3.26, 0.4.0, and 0.4.1. Re-running `briefcase create` on your Briefcase project will result in the updated templates being used. As a workaround, the patch can be added to any existing Briefcase .wxs file generated by Briefcase 0.3.24 or later.

Severity
high
Software
Python
Fixed in
0.3.26
Published
2026-03-26

Affected versions

From: 0.3.0

Until: 0.3.26

Fixed in: 0.3.26

How to fix this CVE

If you use Briefcase to package Python applications as Windows MSI installers, upgrade to Briefcase 0.3.26 or later to patch the privilege escalation vulnerability in per-machine installations. For existing projects, re-run `briefcase create` to regenerate WXS files with corrected permission inheritance settings, or manually apply the security patch to your .wxs file as a temporary workaround.

sudo dnf update python3-briefcase

Defensia detects this vulnerability

How to check if you are affected

  1. Check Briefcase version: python3 -m pip show briefcase | grep Version
  2. Identify Windows MSI projects: grep -r 'msi' .briefcase/ 2>/dev/null || echo 'No MSI projects found'
  3. Review WXS template files: cat build/[project-name]/windows/app/[project-name].wxs | grep -i 'permission\|inherit' to inspect directory permission inheritance
  4. Verify the fix: Regenerate MSI with `briefcase create windows` and confirm the WXS file references InstallScope='perUser' or includes proper permission restrictions; version check should show Briefcase >= 0.3.26

FAQ

What is CVE-2026-33430?

This is a privilege escalation vulnerability in Briefcase's Windows MSI installer template. When developers create per-machine Windows installers, the installation directory inherits parent folder permissions without restriction, allowing low-privileged users to replace application binaries that later execute with administrator rights.

Is CVE-2026-33430 being actively exploited?

No, this vulnerability is not listed in CISA's Known Exploited Vulnerabilities (KEV) catalog and no public exploits are currently available, though the attack requires local system access and user interaction.

What versions of Briefcase are affected by CVE-2026-33430?

Briefcase versions 0.3.0 through 0.3.25 are vulnerable. The issue was fixed in version 0.3.26 and later versions (0.4.0, 0.4.1).

How do I check if my server is vulnerable to CVE-2026-33430?

Run `python3 -m pip show briefcase` and check if the Version is below 0.3.26. If you maintain Windows MSI projects with Briefcase, inspect your .wxs files for proper InstallScope and permission inheritance settings.

Does Defensia detect CVE-2026-33430?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If Briefcase is installed on a monitored server, CVE-2026-33430 will appear in your dashboard with remediation steps.

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References

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